C# Dictionary.ContainsKey()用法及代碼示例

此方法用於檢查字典是否包含指定的鍵。

用法:

public bool ContainsKey (TKey key);

在此，鍵是要在詞典中找到的鍵。

返回值：如果Dictionary包含具有指定鍵的元素，則此方法將返回true，否則返回false。

異常：如果鍵為null，則此方法將提供ArgumentNullException。

以下示例程序旨在說明Dictionary.ContainsKey()方法的使用：

示例1:

// C# code to check if a key is  
// present or not in a Dictionary. 
using System; 
using System.Collections.Generic; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // Create a new dictionary of 
        // strings, with string keys. 
        Dictionary<string, string> myDict =  
          new Dictionary<string, string>(); 
  
        // Adding key/value pairs in myDict 
        myDict.Add("Australia", "Canberra"); 
        myDict.Add("Belgium", "Brussels"); 
        myDict.Add("Netherlands", "Amsterdam"); 
        myDict.Add("China", "Beijing"); 
        myDict.Add("Russia", "Moscow"); 
        myDict.Add("India", "New Delhi"); 
  
        // Checking for Key "India" 
        if (myDict.ContainsKey("India")) 
            Console.WriteLine("Key : India is present"); 
  
        else
            Console.WriteLine("Key : India is absent"); 
    } 
}

輸出：

Key : India is present

示例2:

// C# code to check if a key is  
// present or not in a Dictionary. 
using System; 
using System.Collections.Generic; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // Create a new dictionary of  
        // strings, with string keys. 
        Dictionary<string, string> myDict =  
           new Dictionary<string, string>(); 
  
        // Adding key/value pairs in myDict 
        myDict.Add("Australia", "Canberra"); 
        myDict.Add("Belgium", "Brussels"); 
        myDict.Add("Netherlands", "Amsterdam"); 
        myDict.Add("China", "Beijing"); 
        myDict.Add("Russia", "Moscow"); 
        myDict.Add("India", "New Delhi"); 
  
        // Checking for Key "USA" 
        if (myDict.ContainsKey("USA")) 
            Console.WriteLine("Key : USA is present"); 
  
        else
            Console.WriteLine("Key : USA is absent"); 
    } 
}

輸出：

Key : USA is absent

參考：

https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.containskey?view=netframework-4.7.2

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注：本文由純淨天空篩選整理自rupesh_rao大神的英文原創作品 C# | Dictionary.ContainsKey() Method。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。